As a conventional chlorine dioxide production device and chlorine dioxide production method, ones discloses in e.g. Patent Document 1 identified below can be cited. In this document, there are described a device and a method for generating chlorine dioxide by implementing an electrolytic treatment while supplying an amount of anolyte solution containing chlorite and an amount of catholyte solution containing e.g. sodium hydroxide, sodium chloride etc. to an anode chamber and a cathode chamber respectively of a diaphragm electrolytic cell.